The present invention relates generally to the field of mailing machines, and more particularly to an improved removable and disposable cassette for use in mailing machines which encloses a disposable inked ribbon used in conjunction with a thermal ink transfer printing process by which the mailing machine prints postage indicia on envelopes.
The above referenced patent application discloses and claims a thermal ink ribbon cassette for use in a mailing machine having a postage meter which includes a printing device for printing postage indicia on envelopes passing through the mailing machine. The printing device utilizes thermal ink ribbon printing technology in which thermal ink permeated in a ribbon is heated and deposited in a selected image pattern on the surface of an envelope to form the image of a postage indicia. In its simplest form, this method involves bringing the surface of an envelope and a ribbon that is permeated with a suitable thermal transfer ink into intimate contact, and moving the envelope and ribbon combination beneath a thermal print head which has the capability of heating the inked ribbon selectively along a print line so that the ink is heated and transferred to the surface of the envelope in a desired image pattern. The thermal print head includes a plurality of minute heating elements spaced along a print line which are selectively actuated under the control of suitable software so as to heat the ribbon in a precisely controlled sequence which will produce the desired image on the envelope as the envelope and ribbon are moved together relative to the print head.
As set forth in the above referenced application, thermal ink printing technology is not new and has been successfully utilized in many different applications. But it is relatively new as applied to the printing of postage indicia on envelopes traveling through a mailing machine, and several problems described in the above referenced application were encountered and were addressed by the ink ribbon cassette invention described and claimed therein. Although most of these problems were, for the most part, satisfactorily solved by that invention, some were not entirely solved, and others grew out of that invention, and it is to the solution of these problems that the present invention is directed.
A significant remaining problem is that of breakage of the ribbon during recurring printing operations, and it was determined that the major cause of the breakage was certain conditions that occurred during an excessive amount of contact between the ribbon and the envelopes during a printing operation. There are two aspects to this problem, one being that the ribbon is relatively fragile, and occasionally envelopes are fed into the mailing machine that are wrinkled or curled due to poor manufacture or packaging, or physical or environmental characteristics, with the result that the envelopes can damage the ribbon, and unnecessary contact between the ribbon and the envelopes increases the likelihood of this happening. The other aspect is that due to the fact that the ribbon is moved from the supply spool to the take up spool solely by frictional contact with envelopes moving past the print head, it is virtually impossible to cause the ribbon and the envelopes to move at precisely the same speed, with the result that there is a minute amount of slippage between the contacting surfaces of the ribbon and the envelope. The longer these surfaces are in contact while the ink ribbon and envelopes are moving, the more slippage can occur between the surfaces, with the result that the ribbon can become unevenly wrinkled and eventually skew to one side or the other during further movement, until an edge of the ribbon contacts a portion of the mailing machine or the cassette housing and causes the ribbon to break.
It was also noted that during operation of the prior cassette, occasionally an envelope would tend to remain adhered to the ink ribbon after the ribbon had passed the point where it would normally be separated from the envelope, thereby causing the envelope to jam in the mailing machine. Also, on occasion an envelope would bulge in the middle, either due to overstuffing or physical damage to the envelope, and this would cause it to jam in the mailing machine adjacent the location where the ink ribbon is being separated from it.
Another significant problem that became apparent in the course of using of the cassettes of the prior art is that the anti-reverse mechanism of the take up spool was operable to prevent used ink ribbon from being unwound only when the cassette was in its normal upright orientation, either in its operating position within the cassette or outside of the cassette. Thus, if the cassette was held in an inverted position, or nearly so, a locking gear that was normally held engaged by gravity with a gear on the ribbon take up spool to lock that gear against reverse rotation would become disengaged from the gear, thereby permitting reverse rotation of the gear and the take up spool by pulling on the free end of the ribbon. This defeated a security feature of the cassette, the purpose of which was to prevent unscrupulous users from attempting to reuse the ribbons to obtain duplicate postage indicia for which they had not paid.
Thus, it is apparent that there is a need for further improvement of the cassette disclosed and claimed in the aforementioned prior application to eliminate the remaining problems associated therewith.